Communications signal distribution systems and methods are widely used to distribute a communications signal from at least one communications signal operator to at least one subscriber. For example, cable television (CATV) communications signal distribution systems and methods distribute CATV signals from CATV operators to CATV subscribers. These CATV communications signal distribution systems and methods generally employ a large number of line amplifiers that amplify the communications signal. These systems and methods also generally distribute Alternating Current (AC) power and a communications signal over a coaxial cable having a conductor and a sheath.
In order to reduce the effects of power surges, high voltage spikes, switching transients, power sags, electrical line noise, frequency variations, brown-outs, power failure and/or harmonic distortion on the delivery of the communications signal, it is generally desirable to provide Uninterruptible Power Supply (UPS) systems and methods for the line amplifiers of the communications signal distribution system. These UPS systems and methods may traditionally employ a ferroresonant transformer. See, for example, the brochure entitle CATV Power Solutions, published by LecTro Products Incorporated, Publication No. CSG24FYA, June 1999, and the brochure entitled Lectro Ferro Family, published by LecTro Products Inc., Publication No. CSG16FXA, November 1998.
FIG. 1 is a schematic diagram of a conventional UPS for a communications signal distribution system, that includes a ferroresonant transformer. As shown, the UPS 100 includes a ferroresonant transformer 110, a first primary winding 112 of which is connected between an AC input line 142 and a neutral input line 144 via a utility service entrance box 140, and a resonant secondary winding 116 of which is connected to a coaxial cable 130 having an inner conductor 134 and a sheath 132. A second primary winding 114 of the ferroresonant transformer 110 is connected to a battery 120 via an inverter 122 to provide a “standby” UPS, wherein a transfer switch 150 is used to detect loss of the line voltage input between the input lines 142 and 144, to switch off power to the first primary winding 112 of the ferroresonant transformer and to activate the inverter 122 to power the second primary winding 114 of the ferroresonant transformer.
Still referring to FIG. 1, it can be seen that the input neutral line 144 may be grounded by a pole ground rod, a service ground rod and/or a box ground, and the neutral output line that is connected to the coaxial cable sheath 132 may be grounded by a chassis ground, a cabinet earth ground rod and/or a coaxial sheath ground. The primary and secondary ferroresonant transformer windings 112 and 116, respectively, are interposed between the AC input line 142 and the input neutral line 144, and an output voltage line and an output neutral line 136 that is connected to the sheath 132 of the coaxial cable 130.
Other UPSs for CATV systems are described in U.S. Pat. No. 3,860,748 to Everhart et al. entitled CATV Primary and Auxiliary Power Distribution Apparatus; U.S. Pat. No. 3,909,560 to Martin et al. entitled Method and System for Providing Power to Booster Amplifiers in HF. Cable Network; U.S. Pat. No. 3,916,294 to Kennedy entitled Cable Television Substation Regulated Power Supply With Ripple Suppression; U.S. Pat. No. 4,004,110 to Whyte entitled Power Supply for Power Line Carrier Communication Systems; U.S. Pat. No. 4,724,478 to Masuko et al. entitled Cable Television Communication System With Passive Sensor Signal Path and a Subscriber Power Supply Source; U.S. Pat. No. 5,739,595 to Mekanik et al. entitled Apparatus and Methods for Generating an AC Power Signal for Cable TV Distribution Systems; U.S. Pat. No. 5,747,888 to Zilberberg entitled Back Up System for the Supply of Voltage in Television Cable Systems; and U.S. Pat. No. 5,994,793 to Bobry entitled Uninterruptible Power Supply With Plurality of invertors. Other publications describing UPSs for CATV systems may be found at the website www.multipowerups.com and in a publication entitled Preventing Outages Without Batteries by Bridge et al., CED, June 1999.
Communications signal distribution systems such as CATV systems may be increasingly called upon to distribute Internet, data, telephony and/or advanced video signals. Accordingly, the performance demands for UPS systems and methods for communications signal distribution systems may continue to increase.